Apparatus for coating paper



June 2, 1959 A. H. WELLS ET AL 2,888,902

APPARATUS FOR comma PAPER Filed Nov. 15, 1956 RELATIVELY SOFT SURFACEGATE ROLL 5 COATING MATERIAL FIGJ.

v RELATIVELY HARD SURFACE RELATIVELY APPLICATOR ROLL SOFT SURFACESMOOTHING AND 6 SPREADING ROLLS TRAVELLING WEB RELATIVELY HARD SURFACEGATE ROLl RELATIVELY HARD SURFACE APPLICATOR ROLL RELATIVELY SOFTSURFACE SMOOTHING AND SPREADING ROL-LS RELATIVELY HARD SURFACE APPLKgTORROLL FIG.2.

COATING MATERIAL COATING MATERIAL RE LATIVELY SOFT SURFACE GATE ROLL YRELATIVELY SOFT SURFACE GATE ROLL RELATIVELY SOFT SURFACE SMOOTHING ANDSPREADING ROLLS RELATIVELY SOFT SURFACE SMOOTHING QgE Z TRAVELLING@4344, M was MA I m'maw 5 M BMW 404 41 APPARATUS FOR COATING PAPERArchibald Howard Wells, Gravesend, and William Thomas Crayford,Sittingbourne, England, assignors to The Bowater Research andDevelopment Company Limited, London, England Application November 13,1956, Serial No. 621,782

Claims priority, application Great Britain November 15, 1955 16 Claims.(Cl. 118-227) This invention relates to apparatus for applying a fluidcoating composition to a travelling web of material, such as paper orthe like.

It is known to coat a travelling web of paper or like material by meansof apparatus comprising an applicator roll, a gate roll in contact withsaid applicator roll, whereby the pool of fluid coating material may bemaintained over the nip of said rolls, and one or more rolls in contactwith the applicator roll to spread the coating material across thesurface of the applicator roll. This type of apparatus, using rolls, thesurfaces of all of which are smooth and hard, has the disadvantage thatstriations are formed in the layer of coating material on the applicatorroll prior to being applied to the travelling web of material.

Proposals have been made to prevent the formation of striations byproviding at least one roll in contact with the applicator roll with aheterogenous etched or roughened surface. Although the provision of aroll with a heterogeneous surface satisfactorily prevents the formationof striations in the coating material, it has the disadvantage that thesurface of said roll quickly becomes fouled and clogged with the coatingmaterial which causes irregularities in the layer of coating material onthe applicator roll and necessitates frequent roll washing.

It is an object of the present invention to provide an apparatus whichdoes not have the aforementioned dis advantages.

According to the present invention, apparatus for coating a travellingweb of material comprises an applicator roll, having an even and smoothsurface, adapted to be contacted by the Web in the course of its travel,a gate roll co-operating with said applicator roll to meter the amountof fluid coating material passing through the nip of said rolls and onto the applicator roll, and at least two rolls in contact with theapplicator roll and adapted to smooth and spread evenly the coatingmaterial across the surface of the applicator roll, the gate roll andsmoothing and spreading rolls having an even and smooth surface ofresiliently deformable material which is soft as compared with thesurface of the applicator roll.

Preferably, the gate roll co-operates with the applicator roll on thedown-run side thereof and a pool of fluid coating material is maintainedover the nip of said rolls.

The surface of the gate roll preferably is harder than that of thesmoothing and spreading rolls and the surface of the applicator roll ispreferably of resiliently deformable material.

In the preferred embodiment of the invention the applicator roll, gateroll and smoothing and spreading rolls are provided with surfaces, thehardnesses of which lie within the following ranges as indicated on thePusey and Jones plastometer using a inch ball.

The resiliently deformable material forming the surface Patented June 2,1959 of the various rolls may be natural rubber or a syntheticelastomer, e.g. butadiene polymers or 'copolymers. The gate roll andsmoothing and spreading rolls may be provided with means whereby theirrespective contact pressures on the applicator roll may be adjusted.

A backing roll may be provided in contact with the applicator rollwhereby the web may be passed through the nip of said rolls and thusheld in close contact with the applicator roll. The backing roll may bemounted above or underneath the applicator roll or alternatively may beat the side of the applicator roll. If desired the backing roll may bein the form of another applicator roll so that the web may be coated onboth sides, said applicator roll being associated with a gate roll andsmoothing and spreading rolls as hereinbefore described.

The invention is now described, by way of example, with reference to theaccompanying schematic drawings, in which:

Figure 1 shows in end elevation one arrangement of apparatus forsimultaneously coating a web of material on both sides, roll surfacematerial being shown in section, and

Figure 2 shows an alternative arrangement of apparatus forsimultaneously coating a web of material on both sides, roll surfacematerial being shown in section.

Referring to Figure 1, a pair of rotatable applicator rolls 1 and 2 aremounted one above the other and in contact with each other whereby atravelling web of material 3 may be passed through the nip thereof. Agate roll 4 is positioned in contact with the applicator roll 1 and onthe down-run side thereof is rotatable oppositely to the direction ofrotation of the applicator roll 1, whereby a pool of coating material 5may be maintained over the nip of said rolls. The gate roll 4 isprovided with means (not shown) whereby its pressure contact on theapplicator roll 1 may be adjusted to meter the coating material in thepool 5 on to the surface of the applicator roll 1. By maintaining thegate roll 4 in pressure contact with the applicator roll 1 wetting ofthe surface of the applicator roll 1 is ensured which partly assists inthe prevention of striations in the coating material applied to saidsurface. A pair of smoothing and spreading rolls 6, rotatable oppositelyto the direction of rotation of the applicator roll 1, are positioned inpressure contact with the surfaces of the applicator roll 1 between thegate roll and the nip of the applicator roll 1 with the applicator roll2. The two smoothing and spreading rolls 6 are provided with means (notshown) whereby the pressure can tact with the applicator roll 1 may bevaried. The pressure contact is adjusted, depending upon the type ofcoating material used, so that a layer of coating material of desiredthickness is smoothly and evenly formed on the surface of the applicatorroll. If desired, the two smoothing and spreading rolls 6 and also thegate roll 4 may have peripheral speeds different from that of theapplicator roll but this is not essential and their peripheral speedsmay be the same as that of the applicator roll.

It is pointed out above that the surface of the applicator roll ispreferably of resiliently deformable material, and that the resilientlydeformable material forming the surfaces of the various rolls may benatural rubber or a synthetic elastomer. The applicator rolls 1 and 2may thus be surfaced with such a material, but the specific materialemployed is not critical provided the gate roll 4 and smoothing andspreading rolls 6 have even and smooth surfaces of resilientlydeformable material which is soft as compared with the surface of theapplicator roll 1.

The applicator roll 2 is provided with a gate roll 7 in pressure contactwith said applicator roll whereby a pool of coating material 8 ismaintained over the nip of said rolls. A pair of smoothing and spreadingrolls 9 are positioned in pressure contact with the applicator roll 2between the gate roll 7 and the nip of said applicator roll with theapplicator roll 1. The gate roll 7 and smoothing and spreading rolls 9are provided with means (not shown) to vary the respective pressurecontacts with the applicator roll 2 and they function in a similarmanner as hereinbefore described with regard to the gate roll 4 andsmoothing and spreading rolls 6.

The surfaces of the applicator rolls, gate rolls and smoothing andspreading rolls are formed from natural or synthetic rubber, thehardness of the rubber of the surfaces being graded to lie Within therange quoted hereinbefore.

A pair of heating elements 10 may be provided so that the coatedtravelling web of paper will be partially or completely dried onemerging from the nip of the spplicator rollsl and 2.

An alternative arrangement is shown in Figure 2, which arrangementallows the Web to be coated simultaneously on both sides whilsttravelling vertically. This alternative apparatus is similar to thatshown in Figure 1 except the web is coated whilst travelling verticallyas opposed to horizontally and like reference numerals are used toindicate like components.

The apparatus may beincorporated in a papermaking machine, withoutrecourse to an after process and, although preferably carried out at thestage where the paper has been dried down to approximately 10% or less,by weight of water, it can be used at an earlier stage. The apparatusmay be used to coat a web of paper with any aqueous coating compositioncontaining essentially a mineral pigment and an adhesive. Paper coatedwith such a composition is widely used for magazines, books, periodicalsand the like and also for advertising matter in pamphlet and catalogueform where detailed reproduction is desired.

What we claim is:

1. Apparatus, for coating a travelling web of material, comprising arotatable applicator roll, having an even and smooth surface, adapted tobe contacted bythe web inrthe course of its travel, a gate rollrotatable. oppositely to-the direction of rotation of said applicatorroll and cooperating with said applicator roll whereby a pool of fluidcoating material may be maintained at the nip of said rolls and meteredonto the applicator roll, at least two rolls in pressure contact withthe applicator roll and being rotatable oppositely to the direction ofrotation of said applicator roll and adapted to smooth and spread evenlythe coating material across the surface of the applicator roll, the gateroll and smoothing and spreading rolls having even and smooth surfacesof resiliently deformable material which is soft as compared with thesurface of the applicator roll, and meansfor keeping the web in contactwith said applicator roll.

2. Apparatus according toclaim 1,.wherein the surface of the gate rollis harder than that of the smoothing and spreading rolls.

3. Apparatus, for coating a travelling web of material, comprising arotatable applicator roll, having an even and smooth surface ofresiliently deformable material, adapted to be contacted by theweb inthe course of its travel, a gate roll co-operating rotatable oppositelyto the direction of rotation of said applicator roll and with saidapplicator roll on the down run side thereof, whereby a pool of fluidcoating material may be maintained over, the nip of said rolls andmetered onto the applicator roll, .at least two rolls in pressurecontact with the applicator. roll and being rotatable oppositely to thedirection of rotation of saidapplicator roll and adapted to smooth andspread evenly the coating material across the surface of the applicatorroll, the .gate roll and the smoothing-and spreading rolls havin'g evenand smooth surfaces of resiliently deformable material which is soft ascompared with the surface of theapplicator roll, end means for keepingthe Web in contact with said applicator roll.

4. Apparatus according to claim 3, wherein the applicator roll, gateroll and smoothing and spreading rolls are provided with surfaces thehardnesses of which lie within the following ranges, as indicated on aPusey and Jones plastometer using a% ball:

Applicator roll 35/70 Gate roll -a 70/110 Smoothing andspreading rolls270 5. Apparatus, for coating atravelling web of material, comprising arotatable applicator roll adapted to be contacted bythe'web in thecourse of its travel, a gate roll rotatable oppositely to the directionof rotation of said applicator roll and co-operating with saidapplicator roll on the down run side thereof, whereby the pool of fluidcoating material may be maintained over the nip of said rolls andmetered onto the applicator roll, at least two rolls in pressure contactwith the applicator roll and being rotatable oppositely to the directionof rotation of said applicator roll and adapted to smooth and spreadevenly the coating material across the surface of the applicator roll,all of said rolls having surfaces of resiliently deformable material therespective hardnesses of which lie within the following ranges, asindicated on a Pusey and Jones plastometer using a ball:

Applicator roll 35/70 Gate roll 70/110 Smoothing and spreading rolls190/270 and means for keeping the web in contact with said applicatorroll.

6. Apparatus according to claim 5 wherein the resiliently deformablematerial used to surface the rolls is selected from the group consistingof natural rubber, and synthetic elastomer.

7. Apparatus, for coating a travelling web of material, comprising arotatable applicator roll, having an even and smooth surface, adapted tobe contacted by the web in the course of its travel, a gate rollrotatable oppositely to the direction of rotation of said applicatorroll and co-operating with said applicator roll on the down run sidethereof whereby a pool of fluid coating material may be maintained overthe nip of said rolls and metered onto the applicator roll, at elast tworolls in pressure contact with the applicator roll and being rotatableoppositely to the direction of rotation of said applicator roll andadapted to smooth and spread evenly the coating material across thesurface of the applicator roll, and a backing roll for keeping the webin contact with said applicator roll, whereby the web may be passedthrough the nip of said backing rolls and said applicator roll and thusheld in close contact with the applicator roll, the gate roll andsmoothing and spreading rolls having even and smooth surfaces ofresiliently deformable material which is soft as compared with thesurface of the applicator roll.

8. Apparatus for coating a travelling web of material comprising arotatable applicator roll, having an even and smooth surface ofresiliently deformable material, adapted to be contacted by the web inthe course of its travel, a gate roll rotatable oppositely to thedirection of rotation of said applicator roll and co-operating with saidapplicator roll on the down run side thereof, whereby a pool of fluidcoating material may be maintained over the nip of said rolls andmetered onto the applicator roll, at least two rolls in pressure contactwith the applicator roll and being rotatable oppositely to the directionof rotation of said applicator roll and adapted to smooth and spreadevenly the coating material across the surface of the applicator roll,and a backing roll for keeping the web in contact with said applicatorroll, whereby the web may be passed through the nip of said backing rollandsaid applicator roll and thus held in contact with the. applicatorroll, the gate roll and smoothing and spreading rolls having even andsmooth suraseaooa faces of resiliently deformable material which is softas compared with the surface of the applicator roll, the surface of thegate roll being harder than that of the smoothing and spreading rolls.

9. Apparatus for coating a travelling web of material comprisingrotatable applicator roll adapted to be contacted by the web in thecourse of its travel, a gate roll rotatable oppositely to the directionof rotation of said applicator roll and co-operating with saidapplicator roll on the down run side thereof whereby a pool of fluidcoating material may be maintained over the nip of said rolls andmetered onto the applicator roll, at least two rolls in pressure contactwith the applicator roll and being rotatable oppositely to the directionof rotation of said applicator roll and adapted to smooth and spreadevenly the coating material across the surface of the applicator roll,and a backing roll for keeping the web in contact with the applicatorroll whereby the web may be passed through the nip of said backing rolland said applicator roll and thus held in close contact with theapplicator rolls, the surfaces of all of said rolls being formed ofresiliently deformable material the hardnesses of which lie within thefollowing ranges, as indicated on a Pusey and Jones plastometer using aball:

10. Apparatus according to claim 9 in which the backing roll isunderneath the applicator roll.

11. Apparatus according to claim 9 in which the backing roll is at theside of the applicator roll.

12. Apparatus according to claim 9 in which the backing roll is abovethe applicator roll.

13. Apparatus, for coating a travelling web of material on both sidesthereof, comprising two rotatable applicator rolls each having an evenand smooth surface in contact with each other whereby the web, in thecourse of its travel, may pass through the nip of said rolls, and bekept by each in contact with the other, two gate rolls cooperatingrespectively with each applicator roll, each gate roll being rotatableoppositely to the direction of rotation of the application roll withwhich it cooperates, whereby a pool of fluid coating material may bemaintained at the nip of each applicator roll and its associated gateroll and metered onto the applicator rolls and at least two rolls inpressure contact with each applicator roll and being rotatableoppositely to the direction of rotation thereof and adapted to smoothand spread evenly the coating material across the surface thereof, thegate roll and smoothing and spreading rolls having even and smoothsurfaces of resiliently deformable material which is soft as comparedwith the surfaces of the applicator rolls.

14. Apparatus according to claim 13, wherein the surfaces of the gaterolls are harder than those of the smoothing and spreading rolls.

15. Apparatus, for coating a travelling web of material on both sidesthereof, comprising two rotatable applicator rolls, each having an evenand smooth surface of resiliently deformable material, in contact witheach other whereby the web, in the course of its travel may pass throughthe nip of said rolls and be kept by each in contact with the other, twogate rolls cooperating respectively with each applicator roll on thedown run side thereof, whereby a pool of fluid coating material may bemaintained over the nip of each applicator roll and its associated gateroll and metered onto the applicator rolls, and at least two rollsinpressure contact with each applicator roll, and being rotatableoppositely to the direction of rotation thereof and adapted to smoothand spread evenly the coating material across the surface thereof, thegate rolls and the smoothing and spreading rolls having even and smoothsurfaces of resiliently deformable material which is soft as comparedwith the surface of the applicator rolls.

16. Apparatus according to claim 15, wherein the applicator rolls, gaterolls and smoothing and spreading rolls are provided with surfaces thehardnesses of which lie within the following ranges, as indicated on aPusey and Jones plastometer using a Ms" ball:

